20221721 has 16 divisors (see below), whose sum is σ = 23691024. Its totient is φ = 17086464.

The previous prime is 20221717. The next prime is 20221727. The reversal of 20221721 is 12712202.

It can be written as a sum of positive squares in 8 ways, for example, as 1860496 + 18361225 = 1364^2 + 4285^2 .

It is a cyclic number.

It is not a de Polignac number, because 20221721 - 2² = 20221717 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (17).

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 20221721.

It is not an unprimeable number, because it can be changed into a prime (20221727) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 6941 + ... + 9413.

It is an arithmetic number, because the mean of its divisors is an integer number (1480689).

Almost surely, 2^20221721 is an apocalyptic number.

It is an amenable number.

20221721 is a deficient number, since it is larger than the sum of its proper divisors (3469303).

20221721 is a wasteful number, since it uses less digits than its factorization.

20221721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2540.

The product of its (nonzero) digits is 112, while the sum is 17.

The square root of 20221721 is about 4496.8567911376. The cubic root of 20221721 is about 272.4411499321.

Adding to 20221721 its reverse (12712202), we get a palindrome (32933923).

The spelling of 20221721 in words is "twenty million, two hundred twenty-one thousand, seven hundred twenty-one".